Cathode-ray tube



June 10, 1952 R." B. BARNES 2,599,739

CATHODE-RAY TUBE Filed April 12, 1950 2 SHEETS-Sl-IEET 1 INVENTOR ROBERTBowuue BARNES AT'I'O NEY K W a? 4 E \A //////=a v June 10, 1952 B.BARNES 2,599,739

CATHODE-RAY TUBE Filed April 12, 1950 2 SHEETS-SHEET 2 INVENTOK ROBERTBOWUNG BARNES ATTOKN Y Patented June 10, 1952 CATHODE-RAY TUBE RobertBowling Barnes, Stamford, Conn., assig-nor to American Optical Company,Southbridge, Mass., a voluntary association of Massachusetts ApplicationApril 12, 1950, Serial No. 155,514

13 Claims. 1

This invention relates to cathode ray tubes and has particular referenceto novel means of improving the definition and contrast of imagesproduced on the screens of such tubes.

In conventional types of cathode ray tubes such as used in televisionreceiving apparatus or similardevices images are produced on afluorescent screen when the particles forming said screen are bombardedby an electron beam and are caused to fluoresce in proportion to theintensity of the electrons of said beams. In such a device when afluorescentparticle has been made tofluoresce by the electrons, some ofthe light emitted from said particle isreflected back onto the screenfrom the surfaces of the tube face. This will cause illumination ofother particles of the screen by the light so reflected and produceundesirable halations. Such halations tend to reduce contrast anddefinition of the image formed on the screen.

Therefore, it is a principal object of this invention to provide acathode ray tube with means for reducing halation by eliminating to asubstantial degree the amount of light reflected from the surfaces ofthe tube face onto the fluorescent screen.

Another object is. to provide means for reducing halati'on in a cathoderay tube by providing the outer surface of the tube face with areflection reduction coating for substantially decreasing the amount oflight which may be reflected onto'the fluorescent screen from said outersurface and to simultaneously reduce reflections fromv said surfacecaused by light rays from sources outside the tube.

Another object is to provide the inner surface of the tube face with areflection reduction coating between the material of the tube face andthe fluorescent screen, which coating, due to its naturalcharacteristics, will considerably reduce the amount of reflected lightreaching the fluorescent screen.

Another object is to provide a cathode ray tube with means on theperiphery of the face portion thereof -for preventing light raysstriking said periphery from being reflected back toward the fluorescentscreen, said means being in the form of 'a highly polished surface forpermitting said light rays to escape, or a light absorbing coating onsaid periphery for absorbing the light ra s.

Zinother object is to provide a cathode ray tube with means wherebyfluorescent material on the tube face outside of the desired image areawill be prevented from fluorescing and causing possible additionalhalation within the image area.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings in which:

Fig. 1 is a side elevational view partly in sectionof a cathode ray tubeembodying the inven 7 tion;

Fig. 2 is an enlarged fragmentary sectional view of a portion of thetube face taken on line 22 ofFig.1;

Fig. 3 is a fragmentary side elevational view of the forward end portionof a cathode ray tube; v Fig. 4 is a diagrammatic illustration of lightrays emitted by a fluorescent particle in accordance with conventionalprior art devices of this nature; Fig. 5 is a diagrammatic illustrationof effect of the present invention upon the light rays emitted by afluorescent particle;

Fig. 6 is a fragmentary sectional view of a conventional tube faceadjacent the periphery there: I

of; and

Fig. 7 is a fragmentary sectional view similar to Fig. 6 illustrating afurther feature of the invention.

Referring to the drawings wherein like characters of reference designatelike parts throughout the several views, Fig. 1 illustrates a cathoderay' tube embodying a neck portion [0, substantially I conical sides II, and a face portion [2 all of which may be formed integrally of asuitable glass. However, the sides II and neck Ill may be formed ofmetal and the face portion I! alone formed of glass, if desired,whereupon the glass must be The inner surface suitably sealed to themetal. of the tube face portion I2 is provided with a fluorescent screenI3 composed of a myriad of I fluorescent screen, designated by numeral I4 in Fig. 4, is caused to fluoresce, thelight emitted thereby will passinto and through the glass of the face portion l2 substantially asillustrateddiagrammatically in Fig. 4. Light rays I5 passing through theglass along paths normal to the surfaces of the glass will emerge fromthe outer surface l6 thereof with no deviations. However,

light rays l1 directed through the glass at an angle less than theminimum angle of total re-- partially reflected, as illustrated at 2|emanating from the fluorescent particle M and directed toward the outersurface l6. of the glass at an angle greater than the critical anglewill be totally reflected by the outersu-r'faceilfi and will passrearwardly through the glas's" asindicated by numeral 22 to 'therearsurface 2i! where they will cause illumination of still other particlesMb of the fluorescentscreen whieh a rein optical contact with saidglass. Such light rays which strike the front surface It of the glass atangles greater than the critical angle will be refl' ed; back and" forthfrom the respective of any suitable type which is adapted to reduce 1,

the "am u t org-nightreflected from the surface. S'uch acoating rnay'beany one 'ofthe many well-known types such asisproduced by evaporaf" tionofj'calciuni orother fluorides)- on a glass surface,- br rbrmea bywetting theg'la'ss with 'silicicacidandtreating with hydrochloric acidcopra cipitatefthe silicon dioxide, another-type is made as a film ofb'arium Stearate "which is produced by dipping the glass in Watercontaining barium d ving a layer of 'stearic acid; on 1 top; at ofmagnesium I fluoridegcalcium ee so ium ffiu'orid or? 'sodiurn aluminumstill others are chemical decomposi- 1t a The preferred;- reflectionreduction; coating,

hqweyer; is forifnedj of a composition consisting ollbidal'-'su'spensioncontaining: fromgatout 0. to G-IO per centby weight of sub'microscopic'; micfofgranular; discrete particles 3 of solidanhydifoustransparent material such as magnesium fiucridel- 'lithiumfluoride, strontium fluoride, calciumfluoride, barium fluoride orcr'yolitesubstairtially uniformly dispersed injafvolltile liduid mes othef particles, with the-particles being approximately spherical inshape and l'ess- 'than 625 angstroms in diameter. A-glass surface can 4the concentration of the particles in the irregularities decreasing fromthe surface of the tube face outward, and the material of the particlesbeing such that the effective index of refraction of the coatings variesfrom substantially unity at the layer-air interface to an indexyalueiwhich progressively-increases as it approaches the material of the tubeface portion l2 until it substantially approximates the index ofrefraction of the. glass of the tube face portion. Such a coating willincrease the transmission of light rays-J26 fromthesurface [6 with aconsequent 'de creasein the" reflected light rays 24 (Fig. ascompare'dwith; the normal reflection 19 (Fig. 4). By comparing-Figs. 4 and 5, itwill be understood that by providing the surface 16 with the coating zea negligible amount of light will be reflected toward the fluorescentscreen 13 from light rays striking the surface H5 at angles less than;the: critical angle; Gonsequentlyrparticles Met will manly-slightly ifat-all illuminated b suchlreflections.

In addition, it is. pointedv out; hereihahthe coating 25 will alsopreventreflection ntc an observerfs; eyesof light. rays; strikinel the:tube: face. portion from sources outsidethe tube; This; feature is:particularly desirable r since; it conside erably improves; the.visibility of: the; image 7 To further eliminate, halationstheinnerrsuri faceizo-ofi thetube; face portion Ilmay bBJDZ'Qz: vided witha similanreflection reductiomcoatine; 21;. the-l coating 25.5 being;disposed: between. the; surface: 20 and; they fluorescent screens. 13;

Fi'g. '2:.is a. greatly; enlarged fragmentary; diesgrammatical sectional;view; througlila: portionzof" thetube. face [2: and. diagrammaticallyshows a the coatings 21; arid52-5 provided-on the innertan'douter-surfaces 2'0 and I6 respectively.

surfaces of the tube face. as-a plurality; ofminute irregularities 28each of which is. formed; of: a

plurality of minute particlesxi The fluorescent:

zinc silicate, zinc b'erylliumlsili-cate, zinc cadmium sulphide; zincberyllium tzir'conium silicateg zincborate, I cadmium v tungstate';and-:1 etherv knownr.

materials of mixtures thereof; v

'Itwillbe noted that the particles: M' comprisingthe fluorescent screenare substantially '7 largezithanftl ie' particles 29 "of the reflection'reduction coatings, 'be-ing-from 1 to6' microns in diameter if appliedby spraying. Howevemaa largenpanticles} froni 10 to 3Q microns indiameter are 1 13} deposited on; the screen by dustingor: settl ngthrough air. Thus, when a fluorescentcoatlng I 3f is applied over theinner reflection reduction" coating 2-1; the particles 14 will; due tobe "prpvided with the oeatingby awningw me:-

surface at n layer ofthe abev'e composition 'and subj ectin'g 1 toheatto evaporate the liquid'and mate survcoating of the particleson-'the=surface, 'it beingdesirabletocontrol the 'amount'ofthe-composition-- applied and the concentration offthe' 'particlesin thesuspension so as to produce a ceaunghavmg aresultantthickness of'approximately one quarter wave-length of light;

The forming 1 of i such a coating on I the glass surface will'omprise{sub-microscopic, discrete;

micro 'g'ranula'r transparent solid particles which ar' 'dpositedonthe'gla'sssurface so as reformminute -projecting irregularities onsaid surfac;'

their 1 large size, engage the irregularities 28: in. such fashion thata plurality of vacant spa'cesi 30 'Wi11'Ibe provided between :the'coating-'21 and screen-l3.

Upon- .again on paringFigs- 44:andfiy-liswillfbeis seen thatl halationi'sr'ediiced byapplyifigithereek nection reduction coating 27' "to the'-inner-surface 2 0 pf thetube 'fa'ce portion I 2 3 as describedsi'n'cesthe light rays 21 whichstrike-thesurface-l 6;at

angles greater than the critical angleand are totally reflected backthrough the glass to the: surface Z Othereof willbe' preventedbythe-reflection reduction coating 21 from directly-strik ingf andconsequently illuminating particles; I 417 of"theifinorescent s-creeniItl will beunderstood that if the particles ta-are marred ngagemem i 11;will: be noted that the coatings are disposed 0111131516.;

with the surface 20, as in the conventional cathode ray tube, they wouldbe illuminated by the light rays 22, but by spacing the particles fromthe surface 20, the reflected light rays will be prevented from directlyilluminating the particles. The inner reflection reduction coating 21also greatly minimizes reflection back into the fluorescent material oflight from the inner surface of the glass i2.

Another cause of halation, particularly in the edge areas of the image,is shown in Fig. 6, Wherein the fluorescent screen I3 is disposeddirectly upon the inner surface 20 of the tube face [2 by conventionalmethods which causes a supply of the fluorescent material (3 to bedeposited on the inner surface of the side walls ll of the tube adjacenttheir junction with the face portion i2. l'hus, when fluorescentparticles in this area are made to fluoresce when bombarded by anelectron beam 32, light rays therefrom will pass in all directions andwill, as indicated by lines 3|, illuminate other portions of thefluorescent screen 13, subsequently causing a reduction in contrastdiscrimination in the image. To overcome this, several methods maybeused. For example the fluorescent material in this marginal area may beremoved or covered with a coating of material which would prevent theparticles so covered from being effected by the electron beam, or meansmay be provided internally of the tube for limiting the image area bypreventing the electron stream 32 from striking the fluorescent materialin these areas. Therefore, means such as a ring-like member 33 may beinserted in the tube during the fabrication thereof with the size of thecentral opening of said member 33 being controlled so that the electronbeam 32 will be prevented from striking the fluorescent screen 13 in themarginal areas thereof and thus will limit the size of the desiredeffective image area. Fig. '7 illustrates this feature and shows theelectron beam 32 striking the fluorescent screen l3 at the margin of thedesired image area, with the ring-like member 33 functioning as a baffleor stop for preventing the electron stream 32 from striking thefluorescent material in the marginal area 34 of the screen i3, and thuspreventing undesirable halations from this source.

To reduce further the amount of undesirable light within the material ofthe tube face portion i2 which may be reflected upon the fluorescentscreen l3 .and cause undesirable halations, some of the light rayswithin the glass, particularly in the marginal areas of the face portion12, can be'made to emerge from the glass by providing the outer edge ofthe face portion l2 with a highly'polished peripheral surface 23 (Fig.3). This will permit without diffusion the escape of stray light rayswhich strike this surface at'angles less than the critical angle asshown by dotted lines 22a in Fig. 5. It should be understood that thisportion may be coated on either or both surfaces with reflectionreduction coatings to reduce reflection below the critical angle.

If desired, the peripheral surface 23 may be coated with alight-absorbing material such as a suspension of graphite particles inoil or cement such as Canada balsam, or black lacqueiywhich coatingshould possess an index of refraction equal to or higher than the indexof refraction of the tube face portion I2 for maximum eiflciency.

Thus, light rays 22 (Fig. 5) striking the various surfaces at anglesless than the critical angle may be either'permitted to escape throughthe highly polishedsuri'ace 23 as shown by dotted lines 22a, or maybeabsorbed by the absorbent coating 35.

From the foregoing, it will be seen that means and methods of a novelnature have been employed for accomplishing all of the objects andadvantages of the invention.

While the novel features of the invention have been shown and describedand are pointed out in the annexed claims, it will be understood thatmany changes may bemade in the details shown and described withoutdeparting from the spirit of the invention. I, therefore, do notwish tobe limited to the exact details shown and described as the preferredonly are set forth by way of illustration.

I claim:

l. A cathode ray tube embodying a transparen face portion having acoating of transparent material on the rear surface thereof with acoating of fluorescent material on said transparent material having itseffective portion confined to substantially the area desired of theresultant image and spaced from the inner surface of said transparentface portion by said transparent material, said face portion having atransparent light transmission increasing reflection reduction coatingon the front surface thereof and having light controlling meanssurrounding the periphery thereof, said tube having means forproducreflection reduction coating on the outer surface of thetransparent face portion having an optical thickness and effective indexof refraction such that it, While functioning to reduce reflection ofthe fluorescent material by light rays at angles greater than thecritical angle reflected from the inner side of the front surface of theface portion and said light rays at angles greater than the criticalangle when at the periphery of the face portion being effectivelyobviated by said periph eral light controlling means.

2. A cathode ray tube embodying a transparent 3 face portion having afluorescent screen'adjacent its inner surface, means for producing a thecritical angle, and means forreducing undesirable illumination of saidfluorescent screen comprising a reflection reduction coating dis posedupon the outer surface of said transparentface portion for reducingreflection of light'from sources outside the tube, said reflectionreduction coating being formed of transparent material having an opticalthickness and an effective index of refraction as to simultaneouslyincrease transmission of light rays from said luminous spot by reducingreflections of said light rays emitted by said luminous spot andstriking said outer guyase at angles: lss thani the criticalanei itransparent coatmgionzthednnera surface of saidtransparent face portionfor supporting: said fluorescent screen in spaced; relation. with saidtransparent face portion and reducingmefiections of: lightrays. emittedby 'saidi'luminous spot-amt striking said outer surfaceatiang-Iesgreaten than theicriticat angle; and meansi'om the peripheral edgeof:saidtransparenttftmcaportion for reducew inge. reflection of lightrays: emitted by? said. luminous; spotiand' striking-1 said;peripheraledge;

A'cathoderay 'tube embodyingwtranspa-rent" face portion. havingea:fluorescent: screen? adja-.. cent:itszinnerisurfacezcomposedeofaiplurality' -of contiguously related-particles-of fiuorescent material, means for producing a beam of electrons and directing it uponsaid particles: off: the fluorescent screen: to: produce a luminous spotthereon;- said l'uminousspot emitting" light: rays. StflkiDgE-i the:surfaces OfSQfldif. transparent face, pcntionalt angles both less thanand greater than the critical; angle, andmea-ns rfor'reducingi vdesirable; illumination: of; said fluorescent screen;

comprising. alreflection; reduction coating dis-a p sed. mean heoout rsrface-of saidra spare t ace; uer ionfor reduc nar flection of; li htfrom; our es; u s d h -tube; n fo reducin re flections of light-rays; eni-tted -bysaid luminous spot. and t k ia sa o te ;v su ce; at n les -tan he ri i e r n lez air nsparentcoa r: 1112:4011 theinner surfaceof-said transparent facepqr z nr r ducin v-r flee on l t. aysmitte voyaidiumin u p t n v tr li i J aid ute ii aqeat n les; re er han; h rica e aidt nspar nt c a in omp sin a. layer; of subemigroscopic,discrete, micro-granu- 1; l-irans en 1101 ar i e a; i e en i e -r b r maenmm he flmr s nt. par ic esem t saidicoating} and: approacnestlfeeindexior'refrac tien ofithe material of said face-portion, a seeomrreflection reduction coatingon the-innen surfacel: of- 'said transparentface portion; said seconct re fiection reduction" coating being- -similar to saifl first reflection-'-reductioncoating with the;irregularitiesthereof causing; said fluorescentsereeni to be retained inspaced relation witl i satransparent face portion to reducetneilIHminaJ- tim of the fluorescent. screen by the-light rays emittedxby said-luminous spot 'anet-refiected,15y said' outersurface; and 'meansorrthe-periplieraF edge of said transparent feca -portion for 'r'educing; reflections of light rays" emitted by== said lumimq l g' ndistriking said peripheraledge-w 5;.- A'- cath'cde ray tube'embodying atransparent face portion havinga fluorescent screen adjace itsinner-surfaceaymeansfor producingv atbeam electrons and directing itupon saidTflilorescen screen to produce a; luminous spotthereong. sai

1uminous-- spot-- emitting. lig ht' rays striking the? surfaces of saidtransparent face portionat; angl'esbotliless than-and greaterthanftheecritical" angle, means for rediniing undesirable illuminationiofsaidfluorescent screen comprise-- ing; a reflection reduction coatingdisposed upon the; outer surface of ;sa id transparent face-partion'f'or reducing reflectionoflightr' f rom sources outside thetube andfor increasing-transmission of light rays emitted Icy-said"luminousspotand j striking said outer-surface at, angles-lessthanthew criticalangle;a; transparent coating on theinnen surface; of; said transparentfaoerportiqn for re taining saidjfiuorescent screen-*iirspacedrelationwitli saidtransparent face ortion and; reducing;-

theillurnination of the fluorescent 'screen bglig ht rays emitted by-said lurr'iinousgsp otand reflected r mi ute- -rreaular t eaonaiclinnerS lf w wh ch; cau aid part les-of; efluore cent' is 7 screen, to beretained inspacedrelation with said .nar nt ace er -i ns nd'mean i; nhe; pen b81 11; d e oi said-transparen a e por on: for; udnareflmfiond er y mitte hr luminousi petiaedk sin net. said periph r l 4% e hrxlflway: u e.- emhodit nee; t a p nt acezpo t on,.h yine.z efiuq escen an ada en a nne ur wame ns iq tnred eab m ect qnsaand d req ingszt upon;said. reen 1 0919 14655 uminous p e o r e v. l minous; notxemitinsrsliaht a s 1strik ne;;the; surfaces f; aid; tran par nt facrmttinn-v at. analeszboth e srthanuandlereatertha he r ccal angle, andmeans-for;reduclnggundesiranleumination, of said; uore eentwspr en; mmprse inaaaflrst light trans siominqreasinsz fle t en reduction-coating;Off transparent;- matcrial dis posed: upon-:the quten surf a'ce'ofsaid-transparent face portion-"forreducing reflection, of: lightfrom;sourceszontside thatubeiandiforzincreasing trans:- m-issiom of: light:raysicemittedz; by. 7 said; luminous:v V spotzandt. striking saidiouter; -surface; at; anglesi lessithanalth'e:crlticailrranglessaiddiglit transmi sionainereasingreffection reductionacoatingicomeprisingtgazthm layer- 0f:subemicroscopia; discrete;

fluoresce t;

microf-granulantransparentisolid:particlesqforma l inga minuteirregularities on said-i outer surface,

the concentration of ithe said particles: in: the irregularitiesdecreasing from said outer surf ac'eoutwardlyand the material ofsaidqparticleszbeinga such-that the efiecti-i e-"inden Of refractiOn'ofsaid coating varies--'-from-'sub stantiall unity at the layer-air:interface to -index'-=value which progressively increases in adi-iection inwardly or 75 by .said' outer surface, and means"for=eliminating; some of; the light rays' normally, trapped within.

the material of; said face portion to, prevent re-; fiection thereofontosaid fluorescent-screen com-- rising a highly; polished;outer-surface formed? on .tne peripner *1; :edg of" said, fa'ce portion;forf. permitting; liglot; rays,- striking; said surface: to' erge-1 76f; A catiiodegray tube embodylngja' transparent; face portionhaving; afluoresoentscreen adjacent?- its inuer ur ace; means q ip ll neia"beainrof electri nsaml dire tinaiit u on: said; fluorescent. reen; o. PJZOQLIQJ 9; vlumin nsisp t there nt fiat dzi miIJQ SL PQt' emittin light raysstriking thei ur aces. f; aid transnarent: face; portion at;

n le 'b tliilessg thana rdi reater than ithercriu t means; for dcingirundsirabif. i uminat on; of! said; fluorescent; scr en: compriseing atransparent coating disposedjupon theouter; surface of'saidtrarisparent facanorfion anilineing; an optical thickne sv andeanleff ctive. index. ofretractiontsuchasjo reducerefiection, offliglitj;from sources outside the. tube; andlincreasingthel. transmission of;light 7, rays. emitted. by, said;

minous; spot:andstriking saide outeri surface at;

angles less than the criticaLangle aitransparent;

- t g onsthermnervsnrfaceeofisaifiitran a t' fag-e P- e-- unaqrtina-aaid fluorescent. screen: in spac d re ation-ewitnssaide transparent facen rti niand r ducin thetillumination tuna fluorescentescreen by; ligl tiraysfiemit ed'rb i saidfl umina isn tand'refl ctedibxsaidiooutensurfaeetj nd meansrf reeliminating some ofzthalightnraysnormally trapped within the material of saidsfa'eee por n: to prerntrirefiedfiion:thereof: onto; said. i

v 'ZQ igDt L absorbingzs: maftmaizz disposed; onrthesneriplieran 1.:

fluorescermsereen." omprisin ecoatinea edge of said face portion forabsorption of light rays striking said surface from within.

7. A cathode ray tube embodying a transparent face portion having afluorescent screen disposed adjacent the inner side thereof, means fordirecting electrons -upon said fluorescent screen for producing aluminous spot thereon and a trans-' face portion having a fluorescentscreen disposed adjacent the inner side thereof, means for directingelectrons upon said fluorescent screen for producing a luminous spotthereon, and a light transmission increasing reflection reductioncoating on the outer surface of said face portion which has an opticalthickness and effective index of refraction such as to reducereflections of light from sources outside the tube and to simultaneously increase transmission of light rays emitted by said luminousspot and striking the outer surface of said transparent face portion atangles less than the critical angle, said light transmission increasingreflection reduction coating comprising a thin layer of sub-microscopic,discrete, micro-granular, transparent, solid particles forming minuteirregularities on said outer surface, the concentration of the saidparticles in the irregularities decreasing from said outer surfaceoutwardly and the material of said particles being such that theeffective index of refraction of said coating varies from substantiallyunity at the layer-air interface to an index value which progressivelyincreases in a direction inwardly of said coating and approaches theindex of refraction of the material of said face portion.

9. In a cathode ray tube embodying a transparent face portion having afluorescent screen disposed adjacent the inner side thereof and meansfor directing electrons upon said fluorescent screen for producing aluminous spot thereon, means for reducing halation produced by lightrays emitted by said luminous spot and striking the outer surface ofsaid transparent face portion at angles greater than the critical angleand which are reflected back upon said fluorescent screen comprising atransparent surface reflection reducing coating disposed on said innersurface of the transparent face portion between said inner surface andthe fluorescent screen, said reflection reduction coating comprising athin layer of sub-microscopic, discrete, micro-granular, transparentsolid particles piled in theform of minute irregularities on said outersurface, the concentration of the said particles in the irregularitiesdecreasing from said inner surface in a direction toward the fluorescentscreen and the material of said particles being such that the effectiveindex of refraction of said coating varies from substantially unityadjacent the fluorescent screen to an index value which progressivelyincreases in a direction inwardly of said coating and approaches theindex of refraction of the material of said face portion, the highpoints of said irregularities. engaging said fluorescent screen andmaintaining it in spaced relation with said inner surface to reduceillu- 7 i0 mination of the screen by said reflected light rays.

10. In a cathode ray tube embodying a transparent face portion having afluorescent screen disposed adjacent the inner side thereofand means fordirecting electrons upon said fluorescent screen for producing aluminous spot thereon, said luminous spot having'light rays emanatingtherefrom at angles both less than and greater than thecritical angle,and means for eliminating the major portion of said light rays which areat angles greater than the critical angle comprising a highly polishedsurface on the peripheral edge of said transparent face'portion forpermitting said light rays striking said highly polished surface to passtherethrough.

11. A cathode ray tube embodying a transparent face portion having afluorescent screenadjacent its inner surface, means for producing a beamof electrons and directing it upon said "fluorescent screen to produce aluminous spot thereon, said luminous spot emitting light rays strikingthe surfaces of said transparent face portion at angles both less thanand greater than 1 the critical angle, and means forreducing'undesirable illumination of said fluorescent screen comprisinga reflection reduction coating disposed upon the outer surface of saidtransparent face portion, said coating being formed of a transparentmedium having an effective optical thickness and index of refractionsuch as to reduce reflection of light from sources outside the tube andto reduce reflections of light rays emitted by said luminous spot andstriking said outer surface at angles less than the critical angle whilesimultaneously increasing the transmission of light rays from saidluminous spot through said outer surface, and a transparent coating onthe inner surface of said transparent face portion for maintaining saidfluorescent screen in spaced relation with said transparent face portionfor reducing the illumination of said fluorescent screen by reflectionsof light rays emitted by said luminous spot.

12. A cathode ray tube embodying a transparent face portion having afluorescent screen adjacent its inner surface composed of contiguouslyrelated particles of fluorescent material, means for producing a beam ofelectrons and directing it upon said particles of the fluorescent screento produce a luminous spot thereon, said luminous spot emitting lightrays striking the surfaces of said transparent face portion at anglesboth less than and greater than the critical angle, and means forreducing undesirable illumination of said fluorescent screen comprisinga reflection reduction coating of transparent material disposed upon theouter surface of said transparent face portion and having an effectiveoptical thickness and index of refraction such as to reduce reflectionof light from sources outside the tube and to increase transmission oflight rays emitted by said luminous spot and strikin said outer surfaceat angles less than the critical angle, and a transparent coating on theinner surface of said transparent face portion for reducing theillumination of said fluorescent screen by reflections of light raysemitted by said luminous spot, said transparent coating comprisingarlayer of sub-microscopic, discrete, microgranular, transparent solidparticles of a size substantially smaller than said fluorescentparticles and formin minute irregularities on said inner surface whichcause said fluorescent screen

